The decay of wood and other cellulosic materials by fungi, and the consumption of wood by termites, cause significant economic loss. Until recently, the most widely used wood preservative has been chromated copper arsenate (CCA). However, production of CCA for use in residential structures was prohibited as of January 2004 due to issues raised concerning the environmental impact and safety of arsenic and chromium used in CCA-treated lumber. As CCA replacements, arsenic-free and chromium-free wood preservatives have been developed.
A challenge is obtaining adequate penetration of wood by preservative agents, which typically occurs during pressure treatment of the wood by aqueous wood preservatives. Penetration of an effective amount of preservative agent to adequately protect wood from decay is needed. The acidic CCA wood preservative provides complete and thorough penetration of the preservative agents into wood. However, wood preservatives developed to replace CCA are typically basic systems such as ammoniacal copper quaternary (ACQ). Generally, in basic wood preservative solutions, the typically used copper ion preservative agent penetrates less well. This reduced penetration results in a dramatically decreasing gradient of preservative agent from the surface to the center of a treated article. To establish an effective concentration of preservative agent deep in the wood, high concentrations of preservative agents are needed in the wood preservative solution.
Thus there remains a need for wood preservative compositions which provide improved penetration of the wood preservative agent.